Rhombencephalosynapsis: new findings in a larger study

Abstract

Rhombencephalosynapsis is a developmental midline defect affecting the cerebellar vermis. The absence of the vermis in rhombencephalosynapsis may be compared to the other condition in which the vermis is largely absent. In Joubert syndrome, the cerebellar hemispheres are close to normal in volume; the intervening vermis is small and much shortened, leaving a gap between the cerebellar hemispheres. Although the vermis may also be totally absent in rhombencephalosynapsis, remnants such as the nodule may often be found in their normal place with respect to the adjoining hemispheres. Allowing a simplification, one can describe the vermis in Joubert syndrome as shortened and in rhombencephalosynapsis as narrowed. The debut of the rhombencephalosynapsis story is credited to Obersteiner in 1916 with a detailed case report entitled ‘Ein Kleinhirn ohne Wurm’ (‘A cerebellum without vermis’) describing the autopsy findings in a 31-year old male. The original study is still worth reading for its wealth of detail such as absence of the mesencephalic trigeminal nucleus and misrouting of tracts at the lower mesencephalic level. Over 100 cases have since been published, mostly as case reports or small series. A review lists 58 published cases before …